The present invention relates to utilizing digital dental models to directly manufacture custom tooth die models that can be used as a pattern to fabricate dental prosthetics such as crowns.
In many dental applications, a physical model of a patient's teeth is needed that faithfully reproduces the patient's teeth and other dental structures, including the jaw structure. Conventionally, a three-dimensional negative model of the teeth and other dental structures is created during an impression-taking session where one or more trays are filled with a dental impression material and the tray is then placed over the teeth to create a negative mold. Once the impression material has hardened, the tray of material is removed from the teeth and a plaster like material is poured into the negative mold formed by the impression. After hardening, the poured plaster material is removed from the impression mold and, as necessary, finish work is performed on the casting to create the final physical model of the dental structure. Typically a physical model will include at least one tooth and the adjacent region of gingiva. Physical models may also include all of the teeth of a jaw, the adjacent gingiva and, for the upper jaw, the contour of the palate.
Dental laboratories typically use the physical model as a pattern for the fabrication and fitting of a variety of precision fitted dental prosthetic devices such as crowns, bridges, retainers and veneers. Often, the technician performs a significant amount of work on the physical model to prepare it for use as the pattern for the dental fabrication. For example, when a single tooth crown is to be made, the technician will perform a number of operations to isolate and remove the tooth of interest from the model. First the bottom of the model will be ground flat. The technician will then drill a hole and install a coated pin at the bottom of the tooth model (die) of interest. The pin provides a means of handling the isolated tooth die during the subsequent steps involved in the crown being fabricated. The pinned model is then placed on the top of a base mold tray that has been filled with unhardened plaster material. After the material hardens, the model is now attached to the base form with the coated pin embedded in the base mold. The technician then makes two vertical cuts on each side of the pinned tooth model being careful not to cut or remove material from the tooth model of interest or the adjacent teeth of the model. Because the pin was coated, the plaster material does not adhere to the pin and the cutout tooth die can now be removed from the model/base assembly. The pinned tooth die can now be used as the model to fabricate the crown.
Typically, once the crown has been fabricated, the crown will be installed on the tooth die and placed back on the model/base assembly to verify the fit of the crown with the adjacent teeth in the model. As can be appreciated, the process of cutting the tooth of interest out of the model/base assembly creates the opportunity to damage either the tooth of interest or the adjacent teeth in the model, which results in a potentially poor fitting crown in the patient.
Automated dental structure scanning techniques have been developed as alternatives to the mold casting procedure. Because these techniques can create a direct digital representation of the dental structures, they provide the advantage of creating an “electronic impression” that is immediately transmittable from the patient to a dental Computer Aided Design (CAD) system and, after review and annotation by a dentist, to a dental laboratory. The digital transmission potentially diminishes inconvenience for the patient and eliminates the risk of damage to the impression mold.
For example, U.S. Pat. No. 6,364,660 discloses a method and apparatus for mapping the structure and topography of dental formations such as peridontiun and teeth, both intact and prepared, for diagnosis and dental prosthetics and bridgework by using an intra-oral image scanning technique. As claimed therein, the method can provide a digital 3D model that captures details of orally situated dental formations thus enabling diagnosis and the preparation of precision moldings and fabrications that will provide greater comfort and longer wear to the dental patient.
In parallel with the advancement in the methods and means to create digital dental models, computer aided design (CAD) systems have been developed for use by dental practitioners, which utilize these digital models. Typically, these systems allow the user to view, shift and rotate the digital model as well as perform a variety of measurements. In addition, these CAD systems can transfer files and be interfaced to Computer Integrated Manufacturing (CIM) equipment, such as a CNC milling machine, to fabricate a physical dental model or prosthetic from the digital model file. These CAD systems however do not provide the features needed by dental laboratories to eliminate the manual steps required to create a tooth die.